Acrylate pressure sensitive adhesive, as the term is used herein, refers to tacky acrylate polymer compositions wherein an ester of acrylic acid or methacrylic acid is polymerized, or copolymerized with various comonomers containing a polymerizable ethylenic linkage.
Acrylate and methacrylate pressure sensitive adhesives have many advantageous properties. One of these is their low level of irritation where used in contact with the skin. However, one of the major difficulties with acrylate pressure sensitive adhesives is that when the acrylate or methacrylate polymers are sufficiently soft to possess the required tack or stickiness they are found to have insufficient internal strength to make a completely satisfactory adhesive. As a result, when the adhesive coated article, such for example as an adhesive tape, is removed from an adhered to surface, small particles of the acrylate adhesive tend to still remain. Also, where the adhesive does not have sufficient internal strength, on unwinding strips from a roll of adhesive tape, some of the adhesive is found to transfer to the back of the tape.
The internal strength of the acrylate adhesive can be improved by carrying the polymerization to a higher degree, however, this is found to interfere substantially with the adhesive qualities of the polymer. Also, the internal strength can be improved by use of conventional crosslinking methods such as exposure to electron beam radiation, the addition of peroxide compounds, the inclusion of "self-reactive" pendant groups, such as glycidyl or methylol or the inclusion of "potentially-reactive" groups such as hydroxyl or carboxyl in the polymer. However, here again there is substantial impairment of the stickiness or adhesive qualities of the polymer. For example, electron beam irradiated samples of the acrylate pressure sensitive adhesive, poly (2-ethylhexyl acrylate-co-vinyl acetate), although showing an improvement in internal strength when subjected to doses of 2 megarads, showed a drop in adhesion to human skin of from 70% to 30%.